The present invention relates to a rotary drum cutting head for milling rock or other excavatable terrain and, in particular, to a cutting head that presents cutting implements, such as spirally arranged picks, on a pair of hydraulically driven rotary drums, the cutting drum being driven by a hydraulic motor via a shaft without the interposition of gearing. The invention has particular application as an attachment to a mobile hydraulic plant, such as a hydraulic excavator, backhoe or underground mining machinery.
Conventional rotary drum cutting heads, also known as milling cutters or facing heads, are driven by a hydraulic motor (normally fed with oil under pressure from the hydraulic circuitry of an excavator). One such example uses a multi-gear drive train that rotatably connects the drive shaft of the hydraulic motor (located within the cutting head adaptor for the dipper arm of the excavator) to the driven shaft(s) of the rotary drums. The drive shaft is, as a result, perpendicularly aligned with the driven shaft(s). The drive train itself consists of a train of drive shaft aligned reduction gears acting on a crown wheel and pinion that, in turn, acts on planetary gears for the driven shaft(s).
Due to the many working or moving components of this drive train, some efficiency is lost, such as through friction, and maintenance and overhaul of the drive train can be tedious, time consuming and expensive.
Other examples of prior art rotary drum cutting heads have been the subject of published patents, the following sample of which identify numerous configurations of gears and/or semi-flexible joints utilized hitherto.
U.S. Pat. Nos. 4,172,616 and 4,883,134, GB Patents 1,419,714 and 1,047,472, DE Patent 19,539,249 and SU Patent 1,239,311 all disclose machinery that utilise gears and/or semi flexible joints to transmit energy to the cutting drums.
The cutting drum for a mining machine of U.S. Pat. No. 4,172,616 has two spaced apart body portions, one of which is driven by a shaft of an interior motor through reduction planetary gears. Specifically, this patent describes a single stage planetary gear reduction arrangement in which a sun gear is formed on the shaft, and there is a planet carrier and a stationary ring housing. The planet carrier has a plurality of planetary gears mounted thereon, each of the plurality of planetary gears being in operative association with the sun gear, and the planet carrier operatively connected to the first body portion. The stationary ring housing is operatively connected to a supporting arm and is concentric with an interior of the first body portion. Gear means are formed on the interior of the ring housing. The planetary gears operatively engage the gear means and the sun gear.
The milling apparatus of U.S. Pat. No. 4,883,134 has (in the embodiment of its FIG. 2) two opposed semi-drums rotatably mounted on fixed plates by bearings (such as roller bearings), which rotationally bear against a ring gear fixed to each semi-drum. The motor for the apparatus has a hollow drive shaft with internal grooves which correspond to grooves on a driven shaft which drives the semi-drums. A grooved plate gear fits in grooves at the extremities of driven shaft and rotates in unison with the driven shaft. The circumference of the plate gear is joined to the ring gear or crown of the semi-drum by grooves, whereby rotation of the plate gear causes rotation of its semi-drum through engagement with the ring gear. The grooves serve the purpose of gear teeth or splines to provide a non-reducing 1:1 gear ratio.
In the embodiment of FIG. 3 of U.S. Pat. No. 4,883,134, the semi-drums are made to rotate by a driving gear train turning on shaft joined to bearing support plates. These gears engage, on one hand, in grooves at each extremity of shaft and, on the other hand, on a groove on a ring gear fixed to each semi-drum. By selecting the respective diameters of the shaft and gears, the semi-drums may be made to turn at a different speed to that of motor.
The mining cutting tool of GB 1,419,714 has a hydraulic motor and a gear unit secured thereto. The gear unit has a drive shaft which is provided with a flange opposite to which is a coupling ring fixed to a cutting drum. The flange and coupling ring have apertures which are aligned and distributed about their circumference and which each contain a clamping sleeve having longitudinal slot arrangements that enable the transfer of the moment of rotation from flange to coupling ring.
The mining machine of GB 1,047,472 has a cutter drum and a hydraulic motor for driving the drum. A vertical shaft passes centrally through the drum, and the motor is coaxial about the shaft and has a rotor formed with internal teeth which mesh with an externally toothed portion of the shaft. The drive from the shaft to the drum is effected by a gear wheel keyed on the shaft and meshing with pinions secured on a stub shaft jouralled in a fixed support arm for the vertical shaft. The teeth of pinions engage in respective slots cut in the drum.
The rotary tool for digging trenches of DE 19,539,249 has two coaxially mounted half drums connected to a shaft driven by internal motors. A plate gear, fixed at each end of, and rotatable with, the shaft, is connected by a groove or spline (unnumbered) to a ring gear, supported by bearings, which carry the half drums.
The actuating unit for a cutter SU 1,239,311 has a drum connected to hub by a set of discs mounted on splines of the drum housing and on splines of a cover secured to the hub.
The utilization of gears and/or semi-flexible joints in the above examples of the prior art causes problems in view of the working environment of the cutting drums. Because of the variation of pressure between the workface and the rotating drum which is an inherent result of the design of the mobile hydraulic plant, such as an excavator, the speed of rotation of the drum will vary between slow and fast. Consequently, a major problem with the prior art has been that of gradual, but significant, wearing and damage caused to the gears and/or joints by the frequent backlash experienced when the drum suddenly changes its rotational speed when it interacts with the workface.
It would be beneficial to avoid the use of gears and/or semi-flexible joints altogether so as to prolong the working life and maintenance-free operating periods of rotary drum cutting heads.
GB Patent 1,359,204 discloses a mining cutting tool having a cutting drum which has one or more hydraulic motor of the radial piston type mounted at least partly within the cutting drum and arranged to drive the cutting drum without the interposition of any gears. The hydraulic motors used in this mining cutting tool are of the kind normally utilized for the radial movement and loadings typically required by winches, supported drive shafts and the like that have a slow moving operation and would not be suitable for use in a rotary drum cutting head for milling rock or other excavatable terrain. The mining cutting tool of GB 1,359,204 was subsequently modified in GB 1,419,714 (described earlier) to provide for higher moments of rotation of the cutting drum.
Specifically, the mining cutting tool of GB 1,359,204 has (in the embodiment of its FIG. 1) a pair of hydraulic motors possessing internally located stationary parts (which serve as shafts) and externally located rotating parts. The stationary parts are secured to respective support arms of a forked carrier of a vehicle, which support arms are disposed at opposed external positions of the cutting drum. A cutting drum is flange mounted to each of the rotating parts. The support arms have located therein hydraulic fluid lines. The presence of the external support arms and their housing of the hydraulic fluid lines prevent the embodiment of FIG. 1 being used effectively as a versatile attachment for an excavator (even if the hydraulic motor used for this cutting tool were suitable). For instance, the excavation of trenches and rectangular pits with dimensional precision requires that the cutting implements on the drum be given unimpeded access to the workface so that only the cutting implements make contact with the workface. However, the external support arms would impede access of the cutting drum to confined workfaces and also not allow the cutting drum to be operated shearingly across a workface as the external support arms would got in the way of the cutting drum. In fact, the presence of the external support arms would only allow the cutting drum to have access to a workface from a direction perpendicular to the plane of the workface, and not from a direction parallel to the plane of the workface. Furthermore, the external support arms would physically prevent the excavation of a trench or pit of any substantial depth, and the normal jolting motion of the cutting drum during excavation of an existing trench or pit would cause the external support arms to collide with the walls of the trench and damage not only the arms but also the hydraulic fluid lines located therein.
In the embodiment of FIG. 2 of GS 1,359,204, a cutting head carrier or support arm is centrally located between a pair of drums, each of which is driven by a separate hydraulic motor. Each drum is flange mounted to a rotating part of one of the hydraulic motors which also has a stationary part attached to the carrier. The utilization in this embodiment of separate stationary parts (serving as stationary support shafts) for the motors to support the independent rotation of the rotating parts (serving as rotating output shafts) for each motor upon which a drum is mounted, is technically unacceptable and unsound for a heavy duty excavator attachment. The degree of mechanical instability of the drums with respect to the two stationary support shafts upon which separate hydraulic motors operate would be so high as to compromise the performance of the mining cutting tool. Furthermore, because of the energy imparted by the excavator, the stationary parts should be in one piece, not two, a present consequence of which is that unacceptably low moments of force during the cutting process are transmitted through the shafts to the cutting drums. Also, the presence of a single supply and return circuit for hydraulic fluid means that if one drum experiences significant back pressure sufficient to stop its rotation, the other drum would be accelerated in its rotation, the result of which may be that the accelerated drum exceeds its optimal speed and causes subsequent internal mechanical problems. The stopped drum will remain stationary for so long as the back pressure remains significant, with the consequence that mechanical and hydraulic damage could result.
The embodiment of FIG. 3 of GB 1,359,204 utilizes a single external support arm or cutting head carrier at one side of the single drum. The carrier has fastened thereto a stationary part of a hydraulic motor, the rotating part of the motor being screwed to an intermediate shaft to which the single drum is keyed. The cantilevered nature of this embodiment renders it unsound as an excavator attachment given the imbalance that will arise during operation. Furthermore, the presence of the carrier or external support arm would prevent this embodiment being used effectively as a versatile attachment for an excavator for the same reasons as described with respect to the embodiment of FIG. 1 of GB 1,359,204.
The embodiment of FIG. 4 of GB 1,359,204 has a similar construction to that of FIG. 3 but is mushroom shaped and lacks an external support arm. The screwed attachment of the intermediate shaft to the rotating part (serving as the rotating output shaft) of the motor, and the keying to the intermediate shaft of a bush to which the drum is attached would not be suitable for operating against heavy loads given the two piece nature of the output shaft and the cantilevered drum which is fitted around the intermediate shaft and bush. The shaft is cylindrical and the bush provides a matching cylindrical bore which, because of the slight clearance between the adjacent cylindrical surfaces and the single localized connection of the drum to the shaft, produces a xe2x80x9cfloggingxe2x80x9d force between the bush and shaft, which, over time, allows the drum to seize upon the housing. Indeed, this deficiency in the construction of the mining cutting tool of FIG. 4, which is also present in the miring cutting tool of FIG. 3, was addressed by the modifications made to the tool disclosed in GB 1,419,714, where gears were utilized.
It is an object of the present invention to overcome or at least substantially ameliorate the problems and disadvantages of the prior art.
It is a particular object of the present invention to provide a rotary drum cutting head in which the hydraulic motor driving the drums has a shaft which acts directly, without the involvement of a gear or multi-gear drive train and/or other form of semi-flexible joints to rotate the drums. This object may be achieved by utilizing the drive shaft of the hydraulic motor to rigidly and directly rotatably support the drums, thereby integrating the drive and driven shafts to provide a single integral shaft for rigidly and directly rotatably supporting the drums.
In accordance with the invention, there is provided a rotary drum cutting head comprising a pair of rotary drums which present a plurality of cutting implements adapted for milling rock or other excavatable terrain, and a hydraulic motor having a rotatable output shaft to which the drums are rigidly and directly connected at respective opposed ends of the shaft, wherein the hydraulic motor is centrally disposed between the pair of rotary drums such that the output shaft of the hydraulic motor has a pair of opposed driven ends extending in opposite directions from the motor in longitudinal alignment with the rotational axis of the rotary drums, and wherein the driven ends of the output shaft rotatably support the rotary drums.